As storage mediums used in digital cameras and audio players there are used memory cards called, for example, SD (Secure Digital) Card, Memory Stick, and Multi Media Card. The memory cards are characterized by being as thin as 1.4 to 3 mm or so. Multi Media Card is a generic term for memory cards formed in accordance with a standard published by Multi Media Card Association (MMCA).
In Japanese Published Unexamined Patent Application No. 2000-236043 there is described a warp preventing technique for a COB (chip on board) package which is assembled to a chip card. In this publication there is described a structural example in which a COB package having a sealing member on one surface of a printed circuit board is bonded to a receptacle portion which is a recess formed in one surface of a card body. Reference is also here made to Japanese Published Unexamined Patent Application No. Hei 11(1999)-45959 which describes a technique for preventing the warp of a COB substrate.
Further, in Japanese Published Unexamined Patent Application No. Hei 8(1996)-156470 there is described a technique for preventing the occurrence of breakage in the vicinity of a tip corner of an IC mounting portion upon imposition of a flexural deformation on an IC card. In this publication it is described that when an IC module is bonded with an adhesive into a hole formed in a card substrate, if the IC module is forced into the hole, the adhesive will protrude to the exterior of the hole.
The applicant in the present case has also developed a small-sized memory card called a multi-media card. As shown in FIG. 29(a), this memory card, which is indicated at 1, comprises a card-like cap 2 and a substrate 6, the substrate 6 having a sealing member 5 which is affixed through an adhesive 4 to a stepped recess 3 formed in one surface of the cap 2. The substrate 6 serves as a wiring substrate, and within the sealing member 5 are present plural semiconductor chips (not shown) fixed to the substrate 6 and wires for electrically connecting electrodes formed on the semiconductor chips with wiring lines formed on the substrate.
The sealing member 5 is formed of an insulating resin by transfer molding to improve the productivity. The substrate 6 is formed by a glass fabric-based epoxy resin board. The semiconductor chips are formed of silicon (Si) and the sealing member 5 is formed of an epoxy resin.
A surface of the memory card 1 is located on a back surface 6b side of the substrate 6 affixed to a back surface 2b of the cap 2. The surface portion of the cap 2 exposed framewise around the substrate 6 is the back surface 2b. 
Where required, a film or the like having predetermined printed characters or the like is affixed to the surface 2a of the cap 2 or the back surface 6b of the substrate 6.
It has turned out that there sometimes occurs the following defect in manufacturing the memory card 1. As shown in FIG. 29(b), when the substrate 6 is bonded to the cap 2 with use of the adhesive 4, the back surface 6b of the substrate 5 warps in a depressed state and end portions of the substrate 6 project from an upper surface of the cap 2.
This is caused by a heat distortion based on a difference in thermal expansion coefficient among the substrate 6, the semiconductor chips and sealing member 5 which occurs at the time of radiation of heat after transfer molding and heat curing of the molding resin.
The thermal expansion coefficient of the glass fabric-based epoxy resin board which constitutes the substrate 6 is about 1.3 to 1.6×10−5/° C., that of Si which forms the semiconductor chips is about 3.0×10−6/° C., and that of the epoxy resin which forms the sealing member 5 is about 8 to 16×10−6/° C. As a result, after transfer molding, the sealing member 5 projects toward a surface 6a of the substrate 6 and the back surface 6b of the substrate 6 warps in a centrally depressed state, as shown in FIG. 29(b).
Due to such a depressed warp phenomenon of the back surface 6b of the substrate 6, even if both ends of the substrate 6 are affixed uniformly to the cap 2, they project (projection quantity “a”) from the back surface 2b (upper surface in FIG. 29) of the cap 2. When the memory card 1 is to be used, it is inserted into a slot of a digital camera or the like, but if the projection quantity “a” is large, the projecting portion will be caught in the slot and hence it will become impossible to insert the memory card 1 into the slot. The projection quantity “a” differs depending on the size of the substrate 6, but if the substrate size is, for example, 32 mm long, 23 mm wide, and 1.4 mm thick, the projection quantity “a” is as large as about 150 to 200 μm.
If the substrate 6 is affixed to the cap 2 in an offset manner, an end portion of the substrate warps to a larger extent, as shown in FIG. 29(c). For example, where the thickness of the cap 2 is 1.4 mm, a total thickness “c” is as large as 1.7 mm.
Further, when the substrate 6 is affixed to the cap 2 through the adhesive 4, the adhesive 4 protrudes like arrows from between substrate ends and peripheral edges of the recess 3 of the cap 2, thereby forming raised portions 7. Such a rising phenomenon of the adhesive results in a structure in which an outer surface of the substrate 6 warps in a depressed state. In view of this structure it has turned out that when the substrate 6 is pushed against the cap 2, the warp acts to push out the adhesive 4 present centrally of the recess 3 toward the peripheral edges of the substrate 6 and that therefore the adhesive rising phenomenon becomes easier to occur.
FIG. 30 is a three-dimensional representation of results obtained by measuring a state of warp of a substrate used in a memory card commercially available from A company. In the same figure, longitudinal graduations 0 to 32 are in mm and transverse graduations 0 to 20 are also in mm. Graduations 0 to 1.6 represent the thickness (height) from the surface of the cap and the unit thereof is mm. Also in this example, a central part of a substrate is depressed. Further, it is seen that peripheral edge portions of the substrate project beyond the cap thickness of 1.4 mm.
FIG. 31 represents results of having measured a state of warp of a substrate used in a memory card available commercially from B company, in three-dimensions after image processing. Like the structure shown in FIG. 30, a central part of the substrate is depressed. It is seen that peripheral edge portions of the substrate project beyond the cap thickness of 1.4 mm.
FIG. 32 represents results of having measured a state of warp of a substrate used in a memory card available commercially from C company, in three-dimensions after image processing. In the same figure there is shown an arcuate surface which warps longitudinally of the memory card and projects centrally. Also in this warped state peripheral edges of the substrate project beyond the cap thickness of 1.4 mm. Also in this example it is seen that side edges located near the central part of the substrate further project from the cap.
It is an object of the present invention to provide an electronic device of a structure in which a substrate is affixed through an adhesive to a recess formed in a back surface of a cap, with substrate edges being not projected from the back surface of the cap, as well as a method of manufacturing the electronic device.
It is another object of the present invention to provide a memory card of a structure in which a substrate is affixed through an adhesive to a recess formed in a back surface of a cap, with substrate edges being not projected from the back surface of the cap, as well as a method of manufacturing the memory card.
It is a further object of the present invention to provide an electronic device of a structure in which a substrate is affixed through an adhesive to a recess formed in a back surface of a cap and in which a raised portion caused by flowing out of the adhesive does not occur on the back surface of the cap, as well as a method of manufacturing the electronic device.
It is a still further object of the present invention to provide a memory card of a structure in which a substrate is affixed to a back surface of a cap through an adhesive and in which a raised portion caused by flowing out of the adhesive does not occur on the back surface of the cap, as well as a method of manufacturing the memory card.
The above and other objects and novel features of the present invention will become apparent from the following description and the accompanying drawings.